Glass - Back to the Future!

Presenting Author:
Lawan Umar Grema

article posted 23 March 2016

Lawan Umar Grema is a third year PhD student under the supervision of Prof Russell Hand. Born in 1976 in Nigeria, he obtained his first degree in Mechanical engineering University of Maiduguri, and before starting his PhD he obtained his MSc here in University of Sheffield. Lawan works on sealing glasses for solid oxide fuel cells.

The effects of network formers and modifiers on the thermal and electrical properties of boro-aluminosilicate sealing glasses for Solid Oxide fuel Cells.

Lawan Umar Grema* & Russell J Hand
Department of Materials Science and Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK

Boro-aluminosilicate glasses with additions of lanthanum oxide and/or zinc oxide are potential sealing glasses for planar solid oxide fuel cells (pSOFCs). A system of the form 45SiO2-(10+x) B2O3-5Al2O3-15La2O3-10BaO-(15-x) ZnO glasses (x= 2.5, 5, 7.5, 10) is being investigated. Generally, glass and glass ceramics are the most preferred sealing materials because they meet most of the required properties for sealing through compositional adjustment. These properties include amongst others thermal and electrical properties. Critical thermal properties are first the Tg which should be as low as possible because stresses develop below Tg and released by viscous flow above Tg. Secondly TEC must be greater than 910-6 K-1 so that its compatible with other cell stack components to avoid thermal stress build up in the system leading to cracks and spallation of sealed parts. In addition seals must be electrically non-conductive with resistivity > 104 Ωcm to prevent current shunting. The effect of the network formers and the modifiers on these properties will be established. To achieve the required physical, thermal and electrical properties two series of this composition are characterised. DTA and TMA are being used to assess thermal properties and electrical conductivity is measured by AC impedance spectroscopy. Preliminary results in fig (a) indicates that with increase in heating rate thermal stability of the glass seems to improve and in fig(b) as boron content increases there observed structural changes which will be discussed in the paper.

Figure (a) Tg and Tp shift with heating rates

Figure (b) Structural changes observed in the Raman data.